Summary by cubic

Adds the gen_ai.system attribute (value: "anthropic") to Anthropic spans and logs so token and cost badges render across all requests.

• New Features
  • Added to /v1/messages (sync, async, streaming) and other endpoints (e.g., /v1/complete), including Anthropic Bedrock.
  • Propagated to streaming log events and JSON schema.
  • Updated tests to assert the field and simplify request/response and schema snapshots.

^{Written for commit 8dbf721. Summary will update on new commits.}